1. Field of the Invention
The present invention relates to a light-emitting semiconductor device that emits blue or green light and uses a group III nitride compound. Especially, the present invention relates to the operational whose device characteristics and reliability are improved.
2. Description of the Related Art
It has been known that an aluminum gallium indium nitride (AlGaInN) compound semiconductor may be used to obtain a light-emitting device which emits blue light or another color of light in the short wavelength region. This device is useful because of its high luminous efficiency resulting from direct electron transition and because of its ability to emit blue light, which is one of the three primary colors.
An AlGaInN compound semiconductor layer with p-type conduction can be obtained by doping magnesium (Mg) and irradiating an electron beam thereto or carrying out heat treatment thereto. As a result, a light-emitting diode (LED) with a double hetero p-n junction structure which includes an aluminum gallium nitride (AlGaN) cladding layer of p-type, a zinc (Zn) and silicon (Si) doped emission layer made of indium gallium nitride (InGaN) and a GaN layer of n-type, becomes commercially useful.
This conventional LED has a sapphire substrate on which seven layers are consecutively forced: a buffer layer; an n.sup.+ -layer of GaN heavily doped with Si; a cladding layer of GaN with n-type conduction; an emission layer of InGaN; a cladding layer of AlGaN with p-type conduction: a first contact layer of GaN with p-type conduction; and a second contact layer of GaN with p.sup.+ type conduction. The emission layer is formed to have a 100 nm thickness under the growth temperature of 800.degree. C. The cladding layer is formed to have a 50 nm thickness under the growth temperature of 1100.degree. C. The first contact layer is formed to have a 200 nm thickness under the growth temperature of 1100.degree. C. The second contact layer is formed to have a 50 nm under the growth temperature of 1100.degree. C. It takes about 40 min. to grow the cladding layer and the two contact layers totally.
Still, there exists a problem in luminous intensity of the conventional LED and further improvements are necessary.